The alkyl methacrylate polymers of this invention are characterized by one or more hydroxyhydrocarbyl end groups. The term "polymers" in this context includes copolymers as well. Preparation of these polymers includes the steps of anionic polymerization with an anionic initiator followed by hydrolysis of the initiator end group(s) to create hydroxyl functionality at those positions.
Terminal hydroxy-functional PMMA has been prepared; Simms, "Polymer Science and Technology," V. 11, Klempner and Frisch, ed., Plenum Press, New York, 1980, pages 137 to 152. The preparation consists of initiation of methyl methacrylate polymerization with an azo initiator in the presence of 2-mercaptoethanol chain transfer agent. This process leads to PMMA with about 85% of the chains containing hydroxyl groups, and with a labile sulfur atom linking each hydroxyl to its polymer chain.
U.S. Pat. No. 3,862,100 discloses anionic polymerization initiators containing acetal functions, which initiators can be reacted further to make the initiators employed in the process of this invention. This patent also discloses hydrolysis of bis(acetal-ended) polymers and copolymers of conjugated dienes to the corresponding bis(hydroxyl-ended) polymers.
Wiles and Bywater, Trans. Faraday Soc. 1965, 61, 150, disclose that 1,1-diphenylhexyllithium, made by adding butyllithium to 1,1-diphenylethylene, brings about polymerization of methyl methacrylate in toluene and reacts more preferentially with the C.dbd.C of the methacrylate than with the C.dbd.O. Freyss et al., in Polymer Letters, Volume 2, pages 217 to 222 (1964), disclose use of 1,1-diphenylethylene to get linear styrene/methyl methacrylate block copolymers from "living" polystyrene.
U.S. Pat. No. 3,078,254 discloses coupling of living poly(methyl methacrylate) with organic dihalides. Inaba and Ojima, in Tetrahedron Letters, 1977, No. 23, 2009, disclose oxidative coupling, employing TiCl.sub.4, of methyl isobutyrate through a silyl intermediate. Rathke and Lindert, in J. Am. Chem. Soc., 1971, 93, 4605, disclose treatment of ethyl isobutyrate with lithium cyclohexyl(isopropyl)amide and with CuBr.sub.2 to give coupling to diethyl tetramethylsuccinate.
U.S. Pat. No. 3,639,367 discloses the joining of anionically polymerized hydrocarbon rubbers via oxidative coupling with a monohalogenated hydrocarbon. Hild and Rempp, in C.R. Acad. Sc. Paris, 1969, Series C, 1622 to 1624, and Beinert et al., in Faraday Discuss. Chem. Soc. 1974 (57), 27, disclose the coupling of living poly(methyl methacrylate) employing ethylene dimethacrylate.
Polymerization Mechanisms In General PA0 Monomers PA0 Initiators PA0 Couplers PA0 HPLC Separation
A brief description of vinyl polymerization mechanisms will help place this invention in context. Vinyl polymerizations proceed in more-or-less discrete steps which include all or some of the following:
1. Initiation PA1 2. Propagation PA1 3. Chain transfer PA1 4. Chain branching PA1 5. Termination. PA1 "Methacrylate ester" represents combined units derived from one or more anionically polymerizable methacrylic acid esters in random or block copolymer segments, said esters having the formula CH.sub.2 .dbd.C(CH.sub.3)COOR', where R' is selected from: PA1 (a) alkyl of 1 to 18 carbon atoms, PA1 (b) alkenyl of 2 to 18 carbon atoms, PA1 (c) alkadienyl of 5 to 18 carbon atoms, PA1 (d) dialkylaminoalkyl of 4 to 12 carbon atoms, PA1 (e) alkoxyalkyl of 3 to 12 carbon atoms, PA1 (f) lower fluoroalkyl; PA1 x is a number between 2 and 1000; PA1 Q is selected from hydrogen, a carbon-carbon bond, an m-valent hydrocarbyl radical and a network polymer formed by polymerization of the methacrylate ester of a polyol; PA1 m is 1 when Q is hydrogen, 2 when Q is a carbon-carbon bond, 1 to 6 when Q is a hydrocarbyl radical and more than 1 and up to 100 when Q is a network polymer. PA1 (i) polymerizing one or more methacrylate esters in the presence of an anionic initiator which is the reaction product of (a) an organo(alkali metal) compound having a hydroxyl group blocked by an acetal or ketal function and (b) 1,1-diphenylethylene, and PA1 (ii) hydrolyzing the blocked hydroxyl group of the polymer to effect terminal hydroxyl functionality. PA1 (i) polymerizing one or more methacrylate esters in the presence of an anionic initiator which is the reaction product of (a) an ethylenic double bond-containing organo(alkali metal) compound, and (b) 1,1-diphenylethylene, and PA1 (ii) hydrating the double bond by hydroboration followed by oxidation to effect terminal hydroxyl functionality. PA1 (i) oxidative coupling reagents, PA1 (ii) organic polyhalides, and PA1 (iii) addition coupling reagents.
In an ideal anionic polymerization, the rate of initiation is infinitely faster than the rate of propagation with no chance for chain transfer, branching or spontaneous termination to occur. The steps are schematized in the following equations where In.sup..crclbar. represents the initiating anion (with appropriate counter cation not represented) and M represents a monomer unit: EQU In.sup..crclbar. +M--In-M.sup..crclbar. [Initiation] (1) EQU In-M.sup..crclbar. +nM--In-(M).sub.n+1.sup..crclbar. [Propagation]. (2)
Such polymerizations proceed by a "living" mechanism which is to say that when propagation is complete the anionic terminus of the polymer has a finite lifetime and is capable of adding more monomer of the same or different kind with resultant chain lengthening. The polymerization can then be deliberately terminated in one of several ways if desired. It follows that the degree of polymerization (DP) is determined directly from the ratio of monomer concentration ([M]) to initiator concentration ([In]), and the number average molecular weight of the polymer (M.sub.n) is simply the product of the DP and the monomer unit molecular weight (MW.sub.m) plus the molecular weight of the initiator moiety (MW.sub.In): EQU [M]/[In]=DP (3) EQU M.sub.n =DP.times.MW.sub.m +MW.sub.In ( 4) EQU M.sub.n =[M]/[In].times.MW.sub.m +MW.sub.In
or
The more nearly ideal the system is, the less will be the molecular weight broadening. In the ideal case, the polymer will be monodisperse (M.sub.w /M.sub.n =1+1/DP). Divergence from ideality will increase this ratio. In practice, absolute monodispersity is not achievable but can be closely approached so that M.sub.w /M.sub.n values only slightly greater than the theoretical limit are obtained.
The alkyl methacrylates are a class of monomer amenable to such polymerizations so that, for example, methyl methacrylate (MMA) polymers with M.sub.w /M.sub.n of about 1.01 to 1.1 are possible. Narrow molecular weight distribution copolymers of MMA with other alkyl methacrylates have also been obtained and such manipulations enable one to vary polymer physical properties such as glass transition temperature, hardness, heat distortion temperatures, and the like.
For use in automobile finishes, the polymers must contain functional groups which can participate in crosslinking reactions. Such groups should also afford the possibility of chemical modification so as to provide hardness, flexibility, durability and the like. In methacrylate polymers, these properties can be conferred by providing the polymers with hydroxyl functionality.